Tuesday, August 11, 2009

Tech Tip Tuesday

In my opinion, the humble cabinet scraper gets a bad rap. To appropriate a "Bushism", they are highly misunderestimated. Basically, they are a piece of hardened steel that you turn a burr on the edge of. The burr is the cutting edge and can almost eliminate the use of all but the finest sandpaper in finishing. The cabinet scraper also excels at cutting wild grain where the direction of the grain reverses such as in a burl. They are best on hardwood, but some softwoods can be cut with a scraper so long as you use light pressure.

The scrapers above are a decent selection including some with curves for finishing moldings and different thicknesses. The thicker scrapers are for heavier stock removal and the thinner ones remove a bit less - the closer you get to the final finish, the thinner the scraper I use.

The thing that most people have a problem with is getting a good burr. It's fairly simple, so long as you follow a simple but consistant method I'll show you below. The items below are what I use to maintain my scrapers. On the top is a mill bastard file. This file is used to roughly square the edge. At the bottom is a sharpening stone and some lubricant for dressing the filed edge. The stone is used because the file leaves microscopic cuts which will give you a fragile, slightly serrated edge if you skip the stone before burnishing. The center tool is a polished burnishing tool - basically a very hard piece of steel. Some people use old drill bit shanks for burnishers.

Another thing that I find necessary when using a cabinet scraper is gloves. When using a scraper, you generate heat from friction. It can burn your thumbs and if you haven't built up good callouses, you'll regret not protecting your thumbs!

Here is a sample of typical stock that I use a scraper on. It's a narrow cherry strip for use in the kayak. It's fairly smooth, but you can see the saw marks from resawing this wood.

I pulled out my scraper and started to work. I was raising fine dust. This tells me that the scraper is dull.

So, I first remove the old burrs with the file, keeping the scraper square to the file. Some people use a small block to keep them square.

After the burr was gone, I polished the edge on the sharpening stone until it was perfectly smooth across the whole edge. Again, you want the scraper to be perpendicular to the stone so that you get nice square edges.

Lightly wiping the edge with oil, I then turn the burr in one direction applying firm pressure with the burnishing tool. Note the angle of the burnisher.

I then take the burr that I've created and turn it back at about 10° to create the hooked burr that will do the cutting.

The shavings at the bottom are made with the sharpened scraper. They are fine, lacy shavings that are rolling up in front of the scraper as it is used. As it is used, the scraper is flexed slightly to present a good cutting edge to the wood.

In no time at all, we have a nice smooth surface. This picture was taken at the same point on the strip that the first picture above showing the saw marks. This took less than a minute and maybe 8 passes along the strip. Note the "shine" in the wood and the lack of tool marks. A little bit more finishing; either with a thinner scraper or a fine sandpaper will finish things up and remove the slight fuzz seen on the edge.

If you haven't used a cabinet scraper, you owe it to yourself to try. It takes a bit of practice to get things to work well, but if you persist, I think you will be amazed at how much time and money you'll save.

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